Zeolite beta has been known for over twenty years with its synthesis described in U.S. Pat. No. 3,308,069 and Re. 28,341. U.S. Pat. No. 4,923,690 further discloses the preparation of a highly siliceous and partially crystalline zeolite beta. Generally the procedure for preparing zeolite beta is as described in Re 28,341 which is incorporated by reference and which involves a hydrothermal synthesis from a reaction mixture containing sources of silicon, alumina, a templating cation and water. The as-synthesized zeolite beta typically has a chemical composition on an anhydrous basis in terms of molar oxide ratios of EQU XM.sub.2/n :Al.sub.2 O.sub.3 :YSiO.sub.2
where X has a value from about 0 to about 1.2 and Y has a value from about 20 to about 30.
The as-synthesized zeolite beta can be modified in several ways. For example, it can be dealuminated to provide a zeolite with a higher SiO.sub.2 /Al.sub.2 O.sub.3 ratio or the cations which are contained in the channels of the zeolite can be exchanged for other cations. Applicants have developed a process for modifying an as-synthesized zeolite beta to give a zeolite with unique properties. The process involves first calcining an as-synthesized zeolite beta, then steaming the calcined zeolite and finally treating the steamed zeolite with ammonium ions at a controlled pH of about 1.0 to about 3.5. The resultant zeolite SN-beta is characterized by a unique infrared (IR) absorption pattern which has absorbance maxima at 3780-3785 cm.sup.-1, 3745 cm.sup.-1 (shoulder), 3735 cm.sup.-1, 3675 and 3610 cm.sup.-1, with the 3675 cm.sup.-1 absorbance being smaller than the 3610 .sup.-1 absorbance.
As stated, the art discloses the steaming or dealumination of zeolite beta. Thus, U.S. Pat. No. 5,227,558 discloses steaming a zeolite beta at temperatures of about 550.degree. C. to about 750.degree. C. Further, U.S. Pat. No. 5,139,761 discloses steaming a zeolite omega followed by treating with ammonium ions at low pH. Neither of these references discloses nor hints at applicants' zeolite.